Ultra3 SCSI nears completion

Posted on September 01, 1998

Last month, the SCSI Trade Association (STA) finalized definitions for Ultra3 SCSI, the next generation of the venerable interface. The new interface will double data transfer rates from 80MBps to 160MBps using dual-edge clocking and will offer cyclical redundancy checking (CRC) for increased reliability and data packetization for lower overhead. Other features include low-voltage differential signaling, 12-meter cable lengths, domain validation to identify the configuration and specify the speed, and Quick Arbitration and Select (QAS), which complements packetized SCSI. The interface will be backward compatible with previous generations.

Technically, all of the features are options. However, Skip Jones, vice president of STA and director of planning and technology at QLogic Corp., in Costa Mesa, CA, says most vendors using the Ultra3 moniker will, at a minimum, use CRC and run at 160MBps.

You would think that such features would generate excitement, but the reaction of leading disk-drive manufacturers and industry analysts has been lukewarm. Some point to the fact that the storage market is still absorbing Ultra2 SCSI, while others believe interface transfer rates are already outpacing operating systems` ability to move data. Invariably, however, discussions about SCSI`s future lead to talk about Fibre Channel.

Not surprisingly, some vendors and analysts vacillate about the virtues and future of Ultra3 SCSI in light of Fibre Channel`s emergence. Whether it`s Ultra3 SCSI or Fibre Channel, most observers say interface adoption depends on several factors.

Jim Porter, president of Disk/Trend Inc., a market research firm in Mountain View, CA, offers his initial assessment with tongue in cheek: "Frequently, the most important technical variable is a thing called price."

"How Ultra3 will be used will be application- and costdependent," says Porter. "For example, there are some reduced costs and added convenience with Fibre Channel connectors. If a server includes 10 or 20 drives, connector simplification may lead administrators toward Fibre Channel. On the other hand, humans are creatures of habit and they often stay with the sons and grandsons of things they know--in this case, SCSI."

Ted Deffenbach, director of strategic technical marketing at Quantum in Milpitas, CA, believes Ultra3 will serve as a useful transition technology because of its backward compatibility while Fibre Channel matures. "With the emergence of storage area networks, everyone is using Fibre Channel between the boxes, but inside the boxes users usually want the mainstream SCSI interface, which is reliable, extremely cost-effective, and easy to understand," Deffenbach says. "On the flip side, I don`t want to sound negative about Fibre Channel because we`ve invested heavily in it and plan to bring it out, but we`re waiting for the market to emerge."

Debate also rages about what the storage market really needs. Some observers think Ultra3 and previous SCSI interfaces address current needs, while others maintain you should build for the future.

Dan Good, vice president of research and development for Western Digital`s enterprise storage group in Rochester, MN, believes analysts` market predictions illustrate a distinct need to improve SCSI`s performance as Fibre Channel emerges. "If you look at analysts` data and compare the adoption rates of Fibre Channel and parallel SCSI, Fibre Channel--even all the way out to the year 2001--is expected to be just one third of the market, with two thirds of the market still represented by SCSI. So we do believe there is another turn of the parallel SCSI interface on the horizon," Good adds.

Chuck Neilsen, chief technologist at Fujitsu Computer Products in San Jose, CA, believes the emergence of network-attached storage and SANs are putting a strain on interface bandwidth and operation. "The necessity for higher performance interfaces, whether Ultra2, Ultra3, or Fibre Channel, is being driven by networking and the incredible requirements for storage interconnected with not just one server, but many users of information whether they`re in the same office or around the globe," says Neilsen.

Robert Gray, storage subsystems research manager at International Data Corp., a market research firm in Framingham, MA, agrees that SCSI will satisfy the requirements of lower-end, homogeneous storage environments, but he notes that storage environments rarely stay small. Gray believes Fibre Channel`s characteristics are conducive to--and will better keep up with--today`s rapidly expanding storage environments.

"The number of servers is increasing. There`s a gradual shift toward an increased focus on storage content and supplying that content in different forms, speeds, priorities, and security levels. As you begin to get more content focused, you need multiple connections to the information," says Gray.

"For Ultra3 to succeed, the market has to be ready for it, and most users are still in the stages of implementing Ultra2 right now," says Gerry Humphrey, director of marketing and planning for Seagate Technology`s high-end product and technical group in Oklahoma City.

Harold Mason, STA chairman and director of host marketing at Symbios` Colorado Springs facility, says that while that may be true, setting a specification for Ultra3 "is important so that people know that there is a road map for SCSI."

The ultimate success or failure of Ultra3 SCSI is still speculative. What is not conjecture, according to Fujitsu`s Neilsen, is that storage requirements are bursting at the seams and vendors must continue to work hard to satisfy those requirements.

"When Fibre Channel was first introduced, it delivered an interface data rate that was 10 times faster than the media rate. In the following years, while we were all trying to make Fibre Channel work, we`ve come to the point where the interface rate is only at a factor of two past the media. We need to make more advances in interface data rates and, quite frankly, I think it`s easier to do in serial than in parallel."

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